Thin Film Transistors functioning as switching devices play an important role in the field of display technology.
In general, a thin film transistor comprises at least a gate electrode, a source electrode and a drain electrode (or source-drain electrodes), a channel layer (also called as an active layer) and so on. In recent years, in order to simplify the process flow or reduce the used number of masks, patterns of an active layer, a source electrode and a drain electrode and so on are produced in such a way that a semiconductor layer for manufacture of pattern of the active layer and a conductive layer for manufacture of pattern of the source electrode and the drain electrode are deposited firstly, next, a photoresist pattern with different thicknesses is formed by using a gray tone mask (GTM) or half tone mask (HTM) technology, and finally, an etching process is carried out to produce the patterns of the active layer, a source electrode and a drain electrode, and so on.
With a bottom-gate type TFT as an example, a method for manufacturing the TFT comprises the following steps:                (1) a gate electrode and a gate insulating layer are produced on a substrate;        (2) a semiconductor layer and a conductive layer are deposited on the substrate with the gate electrode and the gate insulating layer formed thereon in sequence;        (3) a photoresist pattern is formed on the conductive layer with a gray-tone mask or a half-tone mask, the gray-tone mask or the half-tone mask being used for realization of a photoresist layer with different thicknesses, so that a thickness of a photoresist at a region of the conductive layer where source and drain electrodes are to be formed and a thickness of the photoresist at a region between the source electrode and the drain electrode are unequal;        (4) etching processes are conducted on the conductive layer and the semiconductor layer successively, so as to form pattern of an active layer, the source electrode and the drain electrode.        